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39 lines
989 B
NASM
39 lines
989 B
NASM
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;------------------------------------------------------------------------------
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;
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; Copyright (c) 2006, Intel Corporation. All rights reserved.<BR>
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; SPDX-License-Identifier: BSD-2-Clause-Patent
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;
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; Module Name:
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;
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; ReadDr4.Asm
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;
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; Abstract:
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;
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; AsmReadDr4 function
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;
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; Notes:
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;
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;------------------------------------------------------------------------------
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SECTION .text
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;------------------------------------------------------------------------------
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; UINTN
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; EFIAPI
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; AsmReadDr4 (
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; VOID
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; );
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;------------------------------------------------------------------------------
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global ASM_PFX(AsmReadDr4)
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ASM_PFX(AsmReadDr4):
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;
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; DR4 is alias to DR6 only if DE (in CR4) is cleared. Otherwise, reading
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; this register will cause a #UD exception.
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;
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; MS assembler doesn't support this instruction since no one would use it
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; under normal circustances. Here opcode is used.
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;
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DB 0xf, 0x21, 0xe0
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ret
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